This invention relates to novel acetanilide yellow dye-forming couplers and to silver halide photographic elements containing them.
A large number of couplers that provide yellow dye images are known. Couplers that form yellow dyes upon reaction with oxidized color developing agents are typically acylacetanilides. They are described, for example, in Bailey and Williams, "The Photographic Color Development Process" in the CHEMISTRY OF SYNTHETIC DYES (K. Venkataraman, ed.), Academic Press, Inc. New York and London, Vol. 4, 341 (1971). Representative couplers are also described in U.S. Pat. Nos. 2,298,443; 2,407,210; 2,875,057; 3,408,194; 3,265,506; and 3,447,928, and in "Farbkuppler--ein Literaturubersicht," published in AGFA MITTEILUNGEN, Band III, pp. 112-126 (1961).
These compounds contain a reactive methylene group as the coupling function, the functional or reactive group common to coupler compounds which reacts with the development product of a primary aromatic amino developing agent. A reactive methylene is a methylene group which is reactive in the coupling process. For example, the methylene group can be present between two negative centers, as in the group --CO--CH.sub.2 --CO--.
Two subclasses of acetanilide yellow couplers are commonly used in color photographic film and paper products. One subclass is based on a pivaloyl acetanilide parent and the other is based on a benzoyl acetanilide parent. The 4-equivalent pivaloyl acetanilide-based couplers possess a high pK.sub.a and do not ionize readily at pH 10. Thus, they generally have low coupling activity. This low activity makes these couplers unsuited for use in reversal films.
In reversal films, the amount of silver used in the products cannot be reduced without adversely affecting the granularity of the image dye. Therefore, since excess silver is present in any event, it is advantageous to use four-equivalent couplers in the case of reversal films. These couplers are cheaper to manufacture and have less chemical bulk, due to the absence of the coupling-off group. This decreased bulk permits thinner coatings for improved optical sharpness. A further advantage is the elimination of the processing scum often associated with two-equivalent couplers and caused by the accumulation of the coupling-off groups in the processing solutions.
Conventional four-equivalent yellow couplers do not have sufficient coupling activity for use in reversal film products. For example, the pivaloyl acetanilide-based couplers require reactivity enhancing coupling-off groups when used in reversal films.